Climate: processes and drivers

What happens in the global climate is mainly determined by a few fundamental processes: incoming solar radiation, characteristics of the earth’s surface, the atmosphere’s ability to retain heat, and the reflectivity of the atmosphere and the earth’s surface. Various mechanisms serve to enhance or weaken the effects of these processes on climate.

Global processes

Albedo effect at sea. A light surface (snow and ice) reflects almost 80% of the incoming energy back to the atmosphere, whereas the dark ocean absorbs heat and reflects only about 10%.

Illustration: Audun Igesund / Norwegian Polar Institute

Radiation

All surfaces radiate energy, often in the form of light. How much and what type of light (infrared, visible, ultraviolet) depends on the surface’s temperature. Surfaces with temperatures common on earth radiate infrared light, whereas the sun is hot enough to radiate visible and ultraviolet light. The warmer the surface, the greater the radiation.

The energy that radiates from the sun creates the basis for weather and climate on earth. The radiation absorbed makes the earth warmer. Unless an equal amount of energy is lost to outer space, the temperature on earth would increase. Earth loses energy to space by radiating infrared light from the surface and the atmosphere. Averaged over the entire globe, the earth loses the same amount of energy in the form of infrared radiation as it takes up from the sun.

For celestial bodies without an atmosphere, such as the moon or Mercury, it is easy to calculate surface temperature based simply on their distance from the sun, their size and how much sunlight they reflect. If the same formula is applied to the earth, the calculated average surface temperature is about ‑17°C. However, the gases in the atmosphere take up much of the infrared radiation emitted from the surface of the earth, which means that the atmosphere grows warmer. The warm atmosphere subsequently emits infrared radiation both out toward space and back to the surface. The infrared light emitted down toward earth warms the surface. This process is called the greenhouse effect, and explains why the earth has an average temperature closer to +14°C than to ‑17°C. Water vapour is the most important greenhouse gas, followed by carbon dioxide (CO2) and methane (CH4).

Climate can change as a result of natural processes or human activities. The most important process behind the ongoing climate change is an increased concentration of CO2 and other greenhouse gases in the atmosphere, which enhance the greenhouse effect. The latest IPCC report summarising available knowledge and evidence shows that the concentration of CO2 in the atmosphere has increased by about 40% since the beginning of the industrial revolution. There are clear indications that human activities have caused this increase. The current atmospheric concentration of CO2 is far higher than any level attained through natural variation over the past 800 000 years, as demonstrated by ice cores, and it is quite certain that the increase in atmospheric CO2 levels seen in the last 100 years has been more rapid than any other increase over the last 22 000 years.[1] Read more about the greenhouse effect and changing concentrations of greenhouse gases at miljøstatus.no.

Greenhouse gases and rising temperature

Fundamental principles of physics decree that an increase in the concentration of greenhouse gases in the atmosphere will lead to higher temperatures on the earth’s surface. The same physical principle can be used to estimate how much the temperature will increase. That is what Svante Arrhenius did way back at the end of the 19th century. He wrote: “On the other hand, any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth’s surface by 4°.”[Världarnas utveckling, 1906]

Modern researchers use climate models that include far more processes and feedback mechanisms than Arrhenius could take into consideration. These models reveal more details concerning where temperatures will rise, how much they will rise, and how factors such as precipitation and sea ice will be affected. Nonetheless, the give essentially the same answer to the question of how much the average temperature will increase at a doubled concentration of CO2: the current estimate is 3.2°C.[2]

Aerosols (tiny particles of soot or sulphates) in the atmosphere can have a cooling effect owing to their ability to refract and absorb incoming solar radiation. The aerosols can also have an indirect effect: they function as condensation nuclei and contribute to formation of clouds. Increased cloud cover increases the earth’s ability to reflect sunlight and thus cools the earth. However, soot in aerosol form also has a warming effect. Read more about soot as a driver of climate at miljøstatus.no. Human activities release many aerosols. The IPCC estimates that overall, man-made aerosols have a cooling effect; in other words, aerosols have lessened the warming we would otherwise have experienced from the increased concentrations of greenhouse gases.[1]

Many other natural processes also influence climate. These processes have led to major climate changes in the past. In the past few million years, the earth has experienced several ice ages, when ice sheets like those that now cover Greenland and Antarctica covered large parts of North America and Europe. These changes were mainly caused by gradual changes in the earth’s orbit around the sun.

Solar radiation varies over an 11-year cycle, and also over longer time scales. The latest IPCC summary of available knowledge and evidence shows that changes in solar radiation have probably contributed very little to the overall changes in climate since the beginning of the industrial era.[1]A few studies show that changes in solar radiation may have contributed to increased global average temperatures during the first half of the 20th century, but have probably played a very minor role in the last half of the century.[3]

The global climate system is also regulated by the energy balance in the oceans and the atmosphere. Global ocean circulation and atmospheric circulation are driven by forces that strive to even out differences in temperature between high and low latitudes. Heat exchange between ocean and atmosphere is an important factor in regional climate patterns. Conditions that influence this balance – such as changes in air and sea temperatures, or cloud and sea ice cover – will thus influence how the climate evolves. On a geological time scale, changes in the shape and location of continents can have strong effects on circulation and heat balance and thus also on global climate. However, given that the continents have been in approximately the same place for the past 500 000 years, this is not a factor of any importance for ongoing climate change.

On geological time scales, the concentrations of greenhouse gases – especially CO2 – change through natural processes. Volcanos emit CO2 to the atmosphere. This release is balanced by processes that capture CO2 in the seabed, and it can be demonstrated in several ways that the increase in atmospheric CO2 levels since the industrial revolution has been caused by human activities.

Ice cores

Glacier ice, particularly the ice in the inland ice sheets of Antarctica and Greenland, holds a treasure trove of information about climate in ancient times. The snow that once fell here contains information about ambient climate hundreds of millennia back in time. Tiny air bubbles trapped in the ice allow scientists to study how the composition of the atmosphere has changed with temperature over time.

One of the most important sources of information in these icy archives is cryptically called δ18O or dD. This is a measure of the relative concentration of different stable isotopes of oxygen in the water the ice crystals are made of. In simple terms, every time water evaporates from the ocean or falls as precipitation, the molecules of water (H2O) that contain certain stable isotopes are more likely to be involved. The exact fraction is temperature-dependent, so if we analyse the snow on the glaciers, we can create a time-line that tells us how temperatures in that area have varied. When this information is stored over long time spans, it becomes a climate archive.

As in all archives, accurate dating is important. Many different methods can be used to calculate the age of an ice core, and several are usually used in parallel. Horizons (layers) formed in conjunction with historic events are important in this context. Volcanic eruptions provide another important way of dating ice cores. Read more.

Solar radiation varies over an 11-year cycle, and also over longer time scales. The latest IPCC summary of available knowledge and evidence shows that changes in solar radiation have probably contributed very little to the overall changes in climate since the beginning of the industrial era.[1]A few studies show that changes in solar radiation may have contributed to increased global average temperatures during the first half of the 20th century, but have probably played a very minor role in the last half of the century.[3]

The global climate system is also regulated by the energy balance in the oceans and the atmosphere. Global ocean circulation and atmospheric circulation are driven by forces that strive to even out differences in temperature between high and low latitudes. Heat exchange between ocean and atmosphere is an important factor in regional climate patterns. Conditions that influence this balance – such as changes in air and sea temperatures, or cloud and sea ice cover – will thus influence how the climate evolves. On a geological time scale, changes in the shape and location of continents can have strong effects on circulation and heat balance and thus also on global climate. However, given that the continents have been in approximately the same place for the past 500 000 years, this is not a factor of any importance for ongoing climate change.

On geological time scales, the concentrations of greenhouse gases – especially CO2 – change through natural processes. Volcanos emit CO2 to the atmosphere. This release is balanced by processes that capture CO2 in the seabed, and it can be demonstrated in several ways that the increase in atmospheric CO2 levels since the industrial revolution has been caused by human activities.

Processes at the poles

Effects of meltwater ponds on sea ice albedo

Research and monitoring done by the Norwegian Polar Institute help improve our understanding of the role of ice in radiation balance. One important field of study is the effect of meltwater ponds on sea ice albedo.[4][5]

Meltwater ponds on ice absorb two or three times more solar energy than exposed, thick sea ice. Research results from the Norwegian Polar Institute imply that meltwater ponds will have a growing impact on total ice melt in the Arctic in the future. Now that the thick multiyear ice is beginning to disappear and a larger proportion of the sea ice is first-year ice, meltwater ponds are more likely to form. One study showed that in July, meltwater ponds covered 77% of the ice, while about 20% of the total ice cover was multiyear ice.

Distinctly polar processes in both north and south, on land (snow, glaciers, and permafrost) and at sea (sea ice, ocean circulation, bottom water formation) ), play a crucial role in the global climate system, acting through complex interactions and feedback mechanisms.

Sea ice is an important factor in maintaining radiative balance in the global climate system through the albedoeffekten. . Snow-covered sea ice reflects about 80% of incoming solar radiation, in contrast to open seas, which absorb more than 90% of incoming solar radiation and reflect only 10% back to the atmosphere. Because of this, changes in the proportion of sea ice and open water have a strong impact on the climate in this region. Record low amounts of sea ice are now being observed repeatedly in Arctic, whereas the extent of sea ice around Antarctica is relatively stable or increasing slightly. Studies suggest that the changes in ice cover in the north over the past decades have contributed to warmer temperatures in the Arctic through much of the year. They also suggest that most of the recent temperature increase in the Arctic can be attributed to reduced sea ice coverage, which in turn influences the formation of sea ice.[6][7] A study from 2010 concluded that the changes in Arctic sea ice extent in the past few years have had less impact on temperature trends outside the region, that is south of 60°N.[8]

Altered ice dynamics and structure, combined with uptake of heat in ice-free seas help enhance the warming of the Arctic and the loss of sea ice. When the heat stored in this reservoir returns to the atmosphere in the autumn and winter, the warmth does not stay in the lower layers of the atmosphere, but rises to higher altitudes, where it influences Arctic wind systems, particularly air exchange between north and south.[9] This is probably a contributing factor in the record low temperatures and record heavy snowfall in southern Europe, along with unusually high temperatures in the Arctic in the winter of 2009-2010.

The Norwegian Polar Institute’s research on sea ice

Research done by the Norwegian Polar Institute contributes toward increased knowledge about a unique climate indicator: sea ice in the Arctic. Under the auspices of the Senter for is, klima og økosystemer (ICE) the Polar Institute studies the physical processes that determine how sea ice evolves in the Arctic.

The project ICE-havis focuses on understanding processes that determine mass and energy exchange – both large-scale and small-scale – between atmosphere, snow, sea ice and ocean, thus increasing our knowledge about how these components interact and which processes control how sea ice evolves.

This is achieved through extensive fieldwork in and around Svalbard, in the Barents Sea and in Fram Strait, and through model simulations using both simple and sophisticated models.

At the poles, cold, dense water is formed, which flows along the depths of the oceans toward the equator; to compensate, other currents form and flow at the ocean surface toward the poles. This is the motor in the ocean circulation system, which in turn regulates global climate. New bottom water forms in only a few areas of the world’s oceans. Global warming can perturb bottom water formation by warming the surface water and increasing the influx of fresh water, both of which decrease the density of the surface water. A considerable proportion of the fresh water in the Arctic Ocean leaves the Arctic with the East Greenland Current through Fram Strait and ends up in the Greenland and Labrador seas, where it can influence the crucial bottom water formation. The Norwegian Polar Institute has been monitoring the fresh water current in Fram Strait since 1997, through permanently deployed instruments and annual research cruises across the current. The Institute reports these monitoring results in MOSJ.

Snow cover, like sea ice cover, is an important factor in maintenance of radiation balance in the global climate system through the albedo effect. On average, about 46 million square kilometres of the earth’s surface is covered with snow every year. But the total area of this snow cover is decreasing, and the period when there is snow cover is getting shorter. The latest IPPC report[1] shows that over the last decades, the area covered by snow has decreased by about 1.6% per decade, and the spring snowmelt is occurring earlier and earlier. Studies imply that the changes in surface temperature that result from changes in snow cover are smaller than those caused by altered sea ice coverage, but are more extensive and prominent in autumn and spring.[10]

Permafrost lies under much of the land in the Arctic, and under the seabed in some places. Permafrost is important for global climate developments because huge amounts of greenhouse gases (mainly methane) lie “locked” inside the frozen ground and could be set free if the permafrost were to disappear. Permafrost is thawing at several locations in the Arctic, and its temperature is now 2°C warmer than it was 20-30 years ago.[11] A monitoring series reported through MOSJ, shows thawing also in Svalbard. So far, however, it has been difficult to calculate the potential magnitude of greenhouse gas emissions from thawing permafrost, because many of the interlinked consequences of such thawing remain poorly understood. The most recent IPCC summary of available knowledge and evidence shows that the best estimate for 2100 is between 50 and 250 gigatonnes of carbon, depending on how global temperature evolves.[1]

The Norwegian Polar Institute’s research on glaciers

Research done by the Norwegian Polar Institute contributes toward increased knowledge about the role Svalbard's glaciers play in the climate system. One topic of study is glacier mass balance – whether glaciers are growing or shrinking overall – and thus what impact they may have on the sea level.

Old ice layers in glaciers can also be used as climate archives and as indicators of the distribution of environmental toxins. Read more about glaciological research.

Glaciers and ice sheets in polar regions influence the climate system in several ways. They too affect radiation balance through the albedo effect , just as sea ice and snow do, but they also have impact on influx of fresh water to the world’s oceans, and thus affect ocean circulation. Almost all the glaciers and ice caps in the Arctic have decreased in volume over the last century; Alaska and northern Canada are the regions that have seen the greatest loss of glacier mass in the past decade.[1] Parallel with this, reduced seawater salinity and density have been observed. It has been estimated that the influx of fresh water (from all sources) has increased by 7700 km3 over the past few years. If this trend continues, there is a risk of changes in major ocean currents, which would in turn have impact on global climate.[11]